Overexpression of FTO alleviates osteoarthritis by regulating the processing of miR-515-5p and the TLR4/MyD88/NF-κB axis.

Abstract

Osteoarthritis (OA) is regarded as the most prevalent chronic joint disease. Fat-mass and obesity-associated gene (FTO) is involved in OA alleviation. This study elucidated the role of FTO in OA and the associated mechanism. We established a cell injury model by stimulating human normal chondrocytes (C28/I2) with lipopolysaccharide (LPS), and measured cell viability, apoptosis, and inflammatory cytokines using CCK-8, flow cytometry, Western blot, and ELISA. TLR4, MyD88, p/t-p65, and p/t-IκBα levels, FTO, COX-2, and iNOS mRNA levels, and m6A methylation levels were measured by Western blot, RT-qPCR, and colorimetry. RNA immunoprecipitation and co-immunoprecipitation were conducted to confirm the interaction between FTO and DGCR8. pri-miR-515-5p process was regulated in an m6A-dependent manner. After predicting the presence of several binding sites between miR-515-5p and TLR4 on Targetscan, we further confirmed their relationship by dual-luciferase assay. OA rat models were established by monosodium iodoacetate injection. The pathological changes in knee joint were observed by HE staining. FTO was diminished in LPS-induced C28/I2 cells. With the increase of LPS concentration, cell viability was repressed, apoptosis rate was increased, and inflammatory markers were promoted, which were annulled by FTO overexpression. FTO interacted with DGCR8 and modulated the pri-miR-515-5p processing in an m6A-dependent manner. miR-515-5p silencing partially averted the inhibitory effect of FTO on LPS-induced cell injury. Given that TLR4 was a direct target of miR-515-5p, miR-515-5p inactivated the MyD88/NF-κB pathway by targeting TLR4. FTO overexpression improved cartilage structure in OA rats, reduced apoptosis, inhibited inflammation in synovial fluid, and repressed the TLR4/MyD88/NF-κB axis. FTO alleviated OA in an m6A-dependent manner via the miR-515-5p/TLR4/MyD88/NF-κB axis.